Comparison of hydrography and circulation on the Newfoundland Shelf during Pages 1990–1993 with the long-term mean

Abstract

Meteorological and ice data from the Atlantic region indicate that the large-scale atmospheric circulation over the Northwest Atlantic during the early 1990s caused below-normal air temperatures in eastern Canada, resulting in increased ice growth during winter, increased ice transport from northern latitudes, and increased freshwater from melting ice during spring. The reduced solar flux onto the ocean surface resulted in a 3-to 4-wk delay in the annual warming cycle causing record low temperatures over the upper water column throughout the Newfoundland Shelf region. We examined temperature, salinity, and current measurements from acoustic Doppler current profilers, moored current meters, and drogued drifting buoys to establish the hydrographic conditions and circulation on the Newfoundland Shelf during 1990-1993 in relation to the longer term (1950-1989) mean. The mean circulation and transport do not show significant departures from the long-term average, but the total advective summer heat transport through the Bonavista transect indicates a 26% reduction during the early 1990s. Résumé : Les données relatives aux conditions météorologiques et à la couverture de glace pour la région de l'Atlantique indiquent que la circulation atmosphérique à grande échelle au-dessus de l'Atlantique Nord-Ouest dans les premières années de la présente décennie a causé, dans l'Est du Canada, des températures de l'air inférieures à la normale, ce qui a entraîné une augmentation de l'englacement durant l'hiver, un accroissement du transport de glace à partir des latitudes nordiques, et une augmentation de la quantité d'eau douce provenant de la fonte des glaces au printemps. La réduction du flux solaire atteignant la surface de l'océan a entraîné un retard de 3 à 4 sem dans le cycle annuel de réchauffement, ce qui a occasionné des records de basse température de l'eau de surface, dans toute la région de la plate-forme de Terre-Neuve. Nous avons étudié les mesures de la température, de la salinité et des courants obtenues grâce à des profileurs de courant acoustiques Doppler, à des courantomètres mouillés et à des bouées dérivantes équipées de drogues, afin de déterminer les conditions hydrographiques et la circulation sur la plate-forme de Terre-Neuve au cours des années 1990-1993 par rapport aux valeurs moyennes établies sur de plus longues périodes (1950-1989). Les moyennes pour la circulation et le transport ne montrent pas d'écarts significatifs par rapport à la moyenne sur 49 ans; par contre, le transport total de chaleur par advection en été sur la section de Bonavista indique une réduction de 26% au début des années 90.

Interannual Variability of the Circulation over the Eastern Canadian Shelf

“…The spatial amplitude S 1 has similar vertical distributions for temperature and salinity anomalies at transect AA ′ , featuring relatively larger values in the top 200 m and smaller values in the lower layer of the transect, with a maximum at about 40 m over the shelf break of the transect. Colbourne et al (1997) revealed an intense southward jet in the top 100 m at Seal Island close to transect AA ′ . This suggests that the southward advection of the interannual variability carried by the offshore branch of the Labrador Current is responsible for the maximum interannual variability in the monthly mean temperature and salinity in the upper layer of the transect shown in Fig.…”

“…The rest of the inner branch and the other two branches flow onto the Newfoundland Shelf. Over the northern Newfoundland Shelf, the Labrador Current has a coastal branch flowing through Avalon Channel to the coastal waters of southern Newfoundland, a middle branch following the shelf break through Flemish Pass, and an eastern branch passing around the seaward flank of Flemish Cap (Petrie and Anderson, 1983;Sheng and Thompson, 1996;Colbourne et al, 1997;Loder et al, 1998;Han et al, 2008). Part of the eastern branch of the Labrador Current over the northern Newfoundland Shelf moves into the deep ocean to join the North Atlantic Current, and the rest joins the middle branch to the south of the Flemish Pass (Han et al, 2008).…”

“…b Interannual Variability in Circulation and Hydrography Circulation and hydrography over the ECS exhibit large interannual variability (Weare, 1977;Petrie et al, 1992;Petrie and Drinkwater, 1993;Colbourne et al, 1997), which could have a significant impact on ecosystem dynamics in the region. There was a massive mortality of "warm-water" tilefish, for example, occurring between April and August of 1882 over the Middle Atlantic Bight.…”

“…Previous studies have demonstrated that the ECS is the most variable area of the North Atlantic and Pacific oceans (Thompson et al, 1988), with the largest seasonal variations in water temperature, about 16°C, occurring over the Scotian Shelf and the Middle Atlantic Bight. Significant efforts have been made in the past to determine the general circulation, hydrographic distributions and associated seasonal variability of the ECS (Smith and Schwing, 1991;Lynch et al, 1996;Sheng and Thompson, 1996;Colbourne et al, 1997;Loder et al, 1998;Xue et al, 2000;Sheng et al, 2001;Han and Loder, 2003;Han et al, 2008). Efforts have also been made to examine the interannual variability over this region (Thompson et al, 1988; Petrie et al, 1992;Petrie and Drinkwater, 1993;Han and Tang, 2001;Han, 2007).…”

Decadal Changes in the Ocean Climate in Newfoundland and Labrador Waters from the 1950s to the 1990s

“…The ocean circulation in the Northwest Atlantic has been described many times (Smith et al, 1937;Peterson, 1987;Greenberg and Petrie, 1988;Chapman and Beardsley, 1989;Lazier and Wright 1993;Petrie and Anderson, 1983;Drinkwater, 1996 andColbourne et al, 1997a). The following brief discussion summarizes the main ocean current features influencing the Newfoundland and Labrador Shelf region.…”